Is stuttering caused by trauma?

Is stuttering caused by trauma? Is stuttering a neurological or psychological thing? Recently, I saw a comment on one of the Reddit posts saying that most stutterers don't stutter when they're alone because the anxiety is gone and then someone commented that stuttering is caused by trauma that associates speaking with negative thoughts. Is that true? I mean I don't remember anything traumatic that caused my stuttering but if it is mainly psychological I would feel better that it's something I can fix rather than a brain thing that I can't fix.